A conventional speaker cabinet 10 is illustrated in FIG. 1. As shown, the speaker cabinet 10 comprises a substantially parallelepiped, hollow case 11 and a cover 12. The hollow case 11 comprises a front opening 110, a top 111, a bottom 111, and a rear 112 in which the top 111 and the bottom 111 are obliquely tapered from a pair of opposite edges of the opening 110 to the rear 112. Two sides 113 of the hollow case 11 are also extended parallel from another pair of opposite edges of the opening 110 to the rear 112. A U-shaped bracket 16 is pivotal about the sides 113 proximate the rear 112. The U-shaped bracket 16 is used to fasten at a predetermined place. A sound control circuit 13 is provided on the inner surface of the rear 112 within the hollow case 11. The sound control circuit 13 is used to receive audio signals from an amplifier of a sound reproducing device (not shown) and control the same. On the cover 12 there are provided a woofer 120, a tweeter 121, and at least one low-frequency sound reflection channel (one is shown) 122. The cover 12 is shaped to snugly fit on the edges of the opening 110. Hence, audio signals of high and low frequencies generated by the sound control circuit 13 are capable of sending to the woofer 120 and the tweeter 121 respectively. The diaphragms of the woofer 120 and the tweeter 121 are thus vibrated to generate low-frequency sounds and high-frequency sounds respectively. Referring to FIG. 1 again, in the prior speaker cabinet 10 a damping member 14 formed of fabric or foam is provided between the cover 12 and the sound control circuit 13. The damping member 14 is used to absorb vibration of low-frequency sounds for avoiding cables 131 and a power cord 132 of the sound control circuit 13 from generating low-frequency resonance. Otherwise, low-frequency sounds may be interfered. Also, a grille-like dusk cover 15 is provided on the cover 12 for the protection of the woofer 120 and the tweeter 121 and is used to prevent dust and other tiny, foreign objects from entering into the speaker cabinet 10.
Referring to FIG. 2, note particularly that in the prior speaker cabinet 10, as stated above, the top 111 and the bottom 111 of the hollow case 11 are obliquely tapered from a pair of opposite edges of the opening 110 to the rear 112. Such design aims at generating an instantaneous vibration on the diaphragm 1201 of the woofer 120 and blowing air inside the hollow case 11 along the oblique inner surfaces of the top 111 and the bottom 111 toward the rear 112 by compressing air inside the case 11 rearward as the diaphragm 1201 moves rearward. Following two equations about ideal air are obtained based on fluid mechanics:A1V1=A2V2, andP1V1=P2V2where A1 and A2 are areas of the front containing the opening 110 and the rear 112 of the hollow case 11 respectively, V1 and V2 are flow rates measured at the front containing the opening 110 and the rear 112 of the hollow case 11 respectively when the diaphragm 1201 of the woofer 120 begins to vibrate, and P1 and P2 are air pressures measured at the front containing the opening 110 and the rear 112 of the hollow case 11 respectively when the diaphragm 1201 of the woofer 120 begins to vibrate. The area A1 of the front containing the opening 110 is much larger than the area A2 of the rear 112 since, as stated above, the top 111 and the bottom 111 of the hollow case 11 are obliquely tapered from a pair of opposite edges of the opening 110 to the rear 112. As such, the flow rate V2 at the rear 112 inside the hollow case 11 is much larger than the flow rate V1 at the opening 110 when the diaphragm 1201 of the woofer 120 vibrates through the application of the above equations. As a result, air dynamic at the rear 112 inside the hollow case 11 is higher.
While higher air dynamic can be obtained at the rear 112 inside the hollow case 11 and also stronger low-frequency resonance of the speaker can be generated when the diaphragm 1201 of the woofer 120 vibrates due to the oblique, taper design of the top 111 and the bottom 111. Also, the top 111 and the bottom 111 of the hollow case 11 are obliquely tapered from a pair of opposite edges of the opening 110 to the rear 112. As such, air, flowed from the front to the rear 112 along the oblique inner surfaces of the top 111 and the bottom 111, may flow back toward the opening 110 when it hits the rear 112 due to the compressibility of air. This is not desired since it may adversely affect the vibration of the diaphragm 1201 of the woofer 120. For solving this problem, at least one low-frequency sounds reflection channel 122 is provided on the cover 12 (or on the rear 112) as best illustrated in the prior speaker cabinet 10 of FIG. 3. The provision of the low-frequency sounds reflection channel 122 is adapted to exit the flowed back air toward the outside.
However, the prior design suffered a disadvantage. In detail, as stated above, the top 111 and the bottom 111 are obliquely tapered from a pair of opposite edges of the opening 110 to the rear 112. Also, two sides 113 of the hollow case 11 are extended parallel from another pair of opposite edges of the opening 110 to the rear 112. That is, four sides 111 and 113 are extended to the rear 112. As such, most air will flow back from the rear 112 to the cover 12 along the same route only a small portion thereof exits from the low-frequency sounds reflection channel 122. The former will cause an adverse vibration of the cover 12, adversely affect the diaphragm 1201 of the woofer 120, and cause distortion in the low-frequency sound. In view of the above, the need for improvement with respect to both quality and volume of low-frequency sounds output of the prior speaker cabinet still exists.